DE2134864A1 - - Google Patents

Description

ON-INQ. OIPt.-ING. M. SC. CIPc-P- (YS. OR. DIPL.-PHVS.

HÖGER - LEGAL RIGHT-GRIESSBACH - HAECKER

PATENT LAWYERS IN STUTTGART

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Texas Instruments Incorporated 135oo North Central Expressway Dallas, Texas, U.S.A.

Radar approach system

The invention relates to a radar approach system for aircraft with an antenna system, a motor for pivoting the antenna around a center point, a radar transmitter and receiver for transmission and receiving pulsed radar signals via the antenna and with a display device.

The invention is thus concerned with a radar system and in particular with a radar approach system, through which a runway approached is recorded and displayed.

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A number of aircraft guidance systems are already known that support the pilot when landing an aircraft. The development of large and very fast jet passenger planes and the development of automatic landing systems such as flight control systems, however, has added to that Desire for an on-board approach system, which is independent of electronic flight control systems of the ground station and at least constant monitoring for the pilot the last part of the approach, touchdown and taxiing out enables. In particular, the desire for an on-board, independent approach monitoring system has emerged, which gives the pilot the positive certainty that the landing course of the aircraft is correct that the aircraft is in the correct position with respect to the runway centerline and threshold lights and that the runway free is. Such an independent approach monitoring system is particularly desirable for take-offs and landings, which take place with little or no visibility at all, as well as when landing on airfields with no or inadequate visibility Navigation aid are equipped.

In-flight radar systems have so far been used to avoid collisions with other aircraft and with the terrain. the however, heretofore developed on-board radar systems have generally been due to antenna resolution and screen image quality not usable as independent landing approach systems. The limits of the reproduction quality of such previously known radar systems Rather, they made reliable decisions for landing, such as detecting the runway and taxiways

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and the precise determination of the angle of the aircraft to the center line the runway impossible. For example, a panoramic device or a PPKPlanet Position Indicator) delivers although a true-to-scale and angular representation of a approached runway, but this representation corresponds to a bird's eye view of the runway, which gives the pilot a wrong A feeling for the altitude and the urgency of the landing process is conveyed and also for difficulties at the moment leads where the pilot takes the approached one instead of the radar image Directly viewed from the runway. On the other hand, the usual B-representation and the delayed B-representation, in which the Distance is recorded over an independent, variable scanning angle, for long distances where the angular distortion is very small, a sufficiently clear picture of the runway, but with the low altitude during landing extreme distortions of the runway display occur, making it impossible for the pilot to see the runway and the To recognize taxiways exactly and which also make it impossible to determine the angle of the aircraft in relation to the center line of the To determine exactly the runway.

The present invention was based on this prior art now the task is based on an on-board radar approach system that is independent of the equipment of the ground stations to propose which one provides a high resolution image at a short distance and during the approach, the touchdown and the run-down of the machine allows precise control of the alignment of the aircraft with respect to the runway, etc.

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This task is described above for a radar approach system Art solved in that an antenna is used with a radiation pattern that is vertical Has spread that is large enough to during the landing approach to recognize the runway and which has a horizontal beam width that ensures high resolution, and further in that circuitry is provided to control the timing of the display device to do so a realistic, perspective picture of the approached Runway supplies on the radar screen.

According to the present invention, an antenna system is also included high resolution combined with a radar screen on which for the pilot in exact agreement with the real one Perspective a realistic, perspective image of the runway being approached is displayed. So it gets the pilot the possibility to see the runway boundaries exactly, accurately determine the angle to the center line of the runway and measure the lateral deviation, and the transition From viewing the screen to viewing the runway directly, there is practically no transition and there are no difficulties with himself.

According to the present invention, there is an on-board, independent one Approach surveillance system from an antenna that can be attached in the aircraft and has a radiation pattern that is sufficiently wide in the vertical direction to recognize a runway when the aircraft is in '

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the final phase of the landing approach, the antenna also having a narrow radiation pattern in the horizontal direction has to provide a high resolution for the detection of the runway. A radar transmitter and receiver is transmitting and receives pulsed radar signals via the antenna. A display device delivers as a function of the output signals of the radar receiver a visual representation of the runway, to a certain extent, approaching the pilot.

In a development of the invention, the antenna is in an aircraft mounted and operable in such a way that it provides radar signals for the detection of a runway during a glide slope approach sends and receives. More precisely, of course, is a radar transmitter and receivers are provided which transmit and receive radar signals via the antenna. A display screen provides one Representation of the runway approached, which corresponds to the actual perspective for the runway from the aircraft.

In a further development of the invention, the invention includes Radar approach system an antenna with an elongated housing, which can be rotated in a horizontal plane in the front part of the Aircraft is attached. The housing carries a waveguide which is slotted at the corners and which is mounted in an elongated horn which is used to align the radiation of the antenna so that there is a smaller beam width in the horizontal direction than results in the vertical direction. To bring about a pivoting movement of the housing, a motor is provided with which Help during the glide slope approach of the aircraft a sufficient

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corresponding horizontal angle is swept over in order to recognize the runway. The inventive radar approach system also contains In a further development of the invention, a display device for the radar system with a screen and with as a function of the radar system controllable circuits for sweeping the screen to generate a visible radar image on the same. More precisely, the circuits control the recording non-linearly and in such a way that the radar image is realistic Perspective.

Preferably the display device comprises a radar picture tube with horizontal and vertical deflection circuits. The above Circuits affect the horizontal deflection circuits corresponding to the horizontal scanning of the radar system. The above said circuits also affect the vertical deflection circuits depending on the ratio of the altitude of the aircraft to the current radar range, so that the approached Runway is depicted in a realistic perspective.

In particular, it has proven to be advantageous if the above-mentioned Circuits affect the horizontal deflection circuits synchronously with the vertical deflection of the radar system. Further it is beneficial if a multitude of wave-shaping circuits generates a shaped output voltage, the amplitude of which varies depending on the altitude of the aircraft. It loads a plurality of memory circuits rely on the voltage given to them by the associated wave-shaping circuits

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is fed. Each of the memory circuits has a different time constant. Circuits are also provided to control the voltages generated by the memory circuits and to provide an output signal for controlling the vertical deflection circuit to generate the radar picture tube, from which the approached runway is shown in the natural perspective

Further advantages and details of the invention are explained in more detail below with reference to a drawing and / or are the subject of the protection claims.
In the drawing show:

1 shows a schematic diagram of the radiation characteristic according to the invention the antenna in the vertical direction during the glideslope approach;

2 shows a schematic representation of the radiation characteristic according to the invention of the antenna in the horizontal Level; {j

3 shows a schematic representation of the arrangement of the inventive Radar approach system in the nose of an aircraft;

U shows a block diagram of the radar approach system according to the invention ;

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5 shows a cross section through the center of the antenna of the invention Systems;

6 shows a plan view of the antenna according to FIG. 5, with individual parts broken away;

FIG. 7 shows a front view of the antenna according to FIG. 5, with individual parts have broken off;

Fig. 8 is a perspective view of part of a slotted Waveguide as used in the antenna according to FIG. 5;

9 shows a block diagram of a control circuit according to the invention for tilting the antenna;

Fig. Io is a block diagram of the radar receiver for the inventive System;

fe Fig. 11 is a block diagram of the radar transmitter for the invention

appropriate system;

Figure 12 is a block diagram of the deflection circuit for the radar picture tube of the system according to the invention;

Fig. 13

and Fig. 14 are schematic representations of the relationship between "aircraft distance and altitude" in the illustration the runway during the glide slope approach;

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Fig. 15

and FIG. 16 are schematic diagrams for explaining the theory of FIG Function of the system according to the invention;

Fig. 17 is a graph showing the relationships among the height angle, the distance and the height in the case of the present invention System;

Figure 18 is a graph of the non-linear stresses for controlling the vertical deflection of the radar picture tube of the system according to the invention;

Fig. 19

a to d idealized representations of the radar screen display during the approach to a runway for an inventive device System;

Fig. 2o a detailed schematic representation of the circuit for generating the non-linear voltage for the Deflection circuit of the system according to the invention;

Figure 21 is a detailed schematic of the delay circuit for generating the light pulse for the tilt generator of the system according to the invention and

22 is a detailed schematic illustration of the latch, hold and summing circuits of the ripple generator of a system according to the invention.

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Figures 1 and 2 show a somewhat schematic representation the basic mode of operation of the radar approach system according to the invention. It is a plane Io during the glide slope approach shown on a runway 12. ■ As Fig. 1 shows, a radar beam is emitted from the nose of the aircraft Io, the vertical beam width 14 of which is approximately 17. As Fig. 2 shows, the horizontal beam width 16 is about 0.4 ° and the beam is continuous over a horizontal scanning angle 18 pivoted from approximately 3o. The pivoting of the radar beam in the system according to the invention enables a high resolution of the radar recording of the approached runway 12 during the landing of the aircraft Io. The ones from the runway 12 and the grass and the ground along the runway reflected signals are from a radar receiver in the nose of the Aircraft Io received, and runway 12 becomes available to the pilot depicted in lifelike perspective.

According to a preferred embodiment of the invention made possible the radar approach system capturing an area of a maximum of about 5 miles, with a range of about 2 miles for the first runway acquisition. The plane Io, which lands with a typical glide slope angle between 2.5 and 3, is thus approximately 2,6oo feet at an altitude of 200 feet away from the end of runway 12 and at the decision height from loo feet to about 1,2oo feet.

3 shows a section of the nose of a conventional aircraft _; around the main components of the inventive radar approach system

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to reveal stems. You can see that in the nose of the A mechanically pivotable antenna 2o is arranged on the aircraft, which antenna has an elongated waveguide 22 slotted at the corners which is pivotable about a vertical axis 24. How out Fig. 2 can be seen, the antenna is periodically pivoted by 15 to both sides of the longitudinal axis of the aircraft Io, in order to obtain a total swivel angle 18 of 3o. In a preferred embodiment, the antenna is 20 per second Pivoted 2.5 times.

By means of suitable, of the housing 28 of the radar transmitter and -Receiver of outgoing connection lines 26 to the waveguide pulse-shaped radar signals are emitted via the antenna 2o. The returning radar signals are received by the receiver received in the housing 2 8. A tilt generator, which is a radar picture tube, is arranged within a further housing 3o 34, which is housed in the dashboard of the aircraft, supplies electrical signals via lines 3 2. The radar picture tube 34 is preferably a direct view spexcher tube and has a screen 36 on which the pilot a realistic, perspective representation of the approaching Detects runway 12. The radar picture tube 34 is with various Control buttons and dial buttons connected, so that the usual B display or a PPI display can be selected as required can be. The energy supply for the entire radar approach system is located in a third housing 38.

The system of the invention is a practical, independent one Radar approach system, which is particularly suitable for use in ir.

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large passenger planes such as jumbo jets. The high resolution of the radar system according to the invention enables the pilot during the final phase of the landing approach even in unfriendly weather, such as rain, snow or fog, if visibility is absolutely zero, the visual estimate of the aircraft's attitude with respect to the runway centerline.

Fig. 4 shows a block diagram of the main components of one according to the invention Radar approach system. The antenna 2o is by means of a switching motor 42 via a rotatable connecting element 4o pivotable. A resolver or transducer 44 determines the instantaneous position of the antenna 2o and delivers it via a line 46 a signal to an antenna position demodulator circuit 48. This demodulator 48 supplies a slowly changing direct voltage, which is fed to an output control circuit 5o, which is used to determine the duty cycle of the voltage pulses that the Switching motor 42 are supplied to influence such that the desired periodic pivoting of the antenna 2o maintained will. For example, when the swing of the antenna 2o becomes smaller, the output control circuit 5o drives the shift motor 42 in such a way that the angle of the antenna pivot is increased again.

The antenna 2o is connected to a radar transmitter 54 and a radar receiver 56 via a circulator 52. The circulator operates as a duplexer and couples the antenna 2o either to the radar transmitter 54 or to the radar receiver 56. A synchronization circuit 58 is used to control the receiver and

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contains a clock generator (not shown) which is an RC oscillator which determines the pulse frequency of the system. Lin monostable multivibrator (not shown) is triggered by the clock generator and determines the pulse frequency of the main trigger of the system. This pulse train is generated via buffer circuits at various points in the system, as will be described in detail below and is hereinafter referred to as PMT.

The pulse train PMT is supplied by the radar transmitter 54 to the deflection generator and in particular the deflection circles 6o for a realistic image and the PPI and B deflection circles 6 2 fed. The deflection circuit 6o for a lifelike reproduction is also supplied with an altitude input signal which the Altitude of the aircraft, and output signals are generated which are applied to the deflection selection circuits 6 4. The deflection selection circuits 64 are controlled via mode switches in a control housing 66. If the realistic When the image is selected, the deflection circles 6o drive for the lifelike image amplifier 68 for the Vertical and horizontal deflection, so that on the direct view storage tube 7o a lifelike, perspective representation is generated. If the control housing 6 6 is the PPI mode is selected, the PPI deflection circuits 62 drive the amplifiers 6 8 for vertical and horizontal deflection such that on the direct view storage tube 7o in a well known manner a panoramic display takes place. When the B display is selected on the control box 66, the B deflection circuit operates

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62 and controls the amplifiers 6 8 for vertical and horizontal deflection in such a way that the usual B display is generated on the direct view storage tube 7q. The energy for the different Parts of the system are supplied from a suitable energy source 72.

The radar receiver 56 is of the quasi-logic type and generates signals which are applied to video amplifier 76 via lines 74. A brightness control and intensity compensation circuit 78 provides the amplifier 75 with a brightness control signal. The video amplifier 76 provides the amplified video and brightness control signals to the beam system supply 8o and controls the intensity of the electron beam of the direct view storage tube 7o. The dashboard mounted intensity regulator 82 controls the gain of the healing control amplifier 76, which in turn controls the brightness of the video information on the direct view storage tube. The storage regulator 82, which is also mounted on the dashboard, is used to regulate the persistence (or storage tent) of the screen image. The storage regulator 82 acts on the erase generator 86 and causes it to supply the counter electrode of the direct view storage tube 7o with a pulse train with a variable duty cycle. This in turn controls the amount of information that is deleted from the storage area of the direct-view storage tube. The erase generator 86 also supplies a pulse that coincides with the erase pulse to a black control tube (not shown) which supplies the voltage for the image supply 88

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drops to a very low level for the duration of the erase pulse. This prevents light surges which would otherwise occur during the duration of the extinguishing pulse. The flood light beam supply system 8H supplies the necessary voltage for the direct storage pipes so that the "flood light beam" is properly bundled. The receiver gain control provides a signal to the receiver 56 so that it changes the amplitude of the radar video signal which is fed to the screen.

The direct view storage tube 7o is of conventional construction, a suitable tube for a radar approach system according to the invention a write speed of USo, ooo inches / microsecond and is manufactured and sold, for example, by Westinghouse Corporation. Basically illuminated the floodlight beam system of the direct view storage tube has a grating which is selectively of the write beam system of the tube is loaded. The tube thus has a glow period that is determined by the pulse duty factor of the extinguishing generator that the Provides pulses to erase the image on the direct view storage tube. The system's light control circuitry prevents one Display during the return time of the deflection circuits.

The light control circuits enable during the active TEiIs the distraction, the writing of video signals and symbols on the screen of the direct view storage tube. The intensity compensation circles 7 8 provide a compensation signal which is superimposed on the light control base pulse and the correction of the

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Differences in deflection speed (inches / microsecond) and the density of radar echoes in different areas of the screen serves. The use of the direct view storage tube 7 o is advantageous in the system according to the invention because the Tube has an integrating effect. Because of this, there is a tendency for weak pulses to be received by the system be, owing to the fact that a large number of hits (Radar echoes) hits the same cell on the screen of the direct view storage tube.

A distance sequence system 9ο receives the clock pulse sequence from a synchronizing circuit 58, the radar video signal from the radar receiver 56 and the antenna position signal from the demodulator 48. The range tracking system 9o generates an indication for the distance of the aircraft from the touchdown point. With the one considered here Embodiment is a number of passive reflectors in the vicinity of the runway in a predetermined pseudo-random Coded placement arranged, and the range following system 9o receives the radar echoes from the reflectors and from these determines the exact distance between the aircraft and the reflectors. This distance following system 9o is in the Details in another application of the applicant (file number ...).

The distance information received from the distance following system 9o is supplied to the amplifiers 76 for display on the direct view storage tube 7o to the pilot. The distance information is also assigned to a glide slope calculator 9 2

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which leads to the relative amplitudes of the given by the Set up along the runway reflectors reflected radar echoes determined and a display of the position of the Aircraft relative to the runway glideslope. These indications are fed to the amplifiers 76. A detailed representation of the glideslope computer can be found in another application of the applicant (file number ...).

Antenna system

Figures 5 to 7 show the antenna arrangement 2o. An essentially cylindrical element loo is suitable for being rigidly connected to a radome bulkhead in the nose of an aircraft. A housing Io2 is connected to the cylindrical element loo and carries the pivotable antenna arrangement. A lower one Housing Io4 contains a swiveling connecting element 1ο6, which is a pivot between a fixed waveguide section Io8 and one connected to the pivotable antenna Waveguide section Ho allows. The wave conductor section Io8 is connected to the radar transmitter and receiver of the invention Systems connected. The entire waveguide assembly of the system is normally under pressure from Frigen 116. A Measuring transducer 111 is connected to a switching motor, which consists of a rotor 112 and a housing 114 with the stator. The transducer 111 supplies a signal that is dependent on the position of the antenna to the antenna control loop, which has already been mentioned above has been described so that these in turn send signals to the switching

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motor supplies to the desired pivoting movement of the antenna to maintain.

The outgoing shaft 116 of the shift motor is supported in bearings 118 and firmly connected to the housing 12o of the antenna, the pivoting movement of which it brings about. At the top of the case 124, which is screwed onto the housing3o2, is a Shaft 122 attached. With the pivotable antenna, an outer housing 126 is also connected, which in bearings 12 8 and 13o is mounted so that it is opposite the fixed housing of the antenna system is pivotable. At the lower end of the shaft 122 a substantially U-shaped element 13 2 is attached, in which the center piece of an elongated leaf spring 134 is supported. A screw 136 allows the legs of the U-shaped Element 132 to pull against each other and thus to clamp the center of the leaf spring 134 securely. As best seen in Fig. 6 is clear, the leaf spring 134 extends over the entire length of the antenna housing 12o. The ends of the leaf spring 134 are not clamped, but rather movable between pairs of rollers 14o and 142 at the two ends. When the antenna housing is pivoted, the leaf spring 134 bends and moves relative to the roller pairs 14o and 142. In the Pivoting the antenna housing stores the leaf spring 134 energy and tries to return the housing to its starting position.

A rear housing part 146 is connected to the housing 12o and is designed for an aerodynamic or streamlined design

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the antenna. A radome 14 8 is also attached to the front of the housing 12o. Preferably, the radome 14 consists of 8 made of a material such as fiberglass, which is transparent to radar signals.

A horn antenna 15o is attached to the front of the antenna and encloses a waveguide 152 along it entire length. The waveguide 152 is connected to the waveguide section Ho. In the horn antenna 15o is a polarizer 154 of the quarter-wavelength grating type, which preferably consists of foamed-in-accordance with dielectric material. A support element 156 is also connected to the horn antenna 15o.

As FIG. 6 shows, the antenna is rotated 30 about the vertical axis of the shaft 122 or starting out during operation from the middle position by 15 to both sides. The leaf spring 134 supports the pivoting movement of the antenna and the error signal supplied by the transducer via the control circuit to the switching motor ensures that the pivoting movement of the antenna is maintained over the specified angular range. In a preferred embodiment of the antenna this is about 6o inches long and 7 inches wide. The antenna of the system according to the invention is also preferably in the Ka-band operated between 3 3 and 3 8 GHz. With an antenna loss of 2.5 dB, the antenna gain is in a preferred embodiment at about 3 3.5 dB.

The antenna according to the invention is of the type with one at the corners

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Slotted waveguide. In this context, reference is made in particular to FIG. 8, which shows a section of a shows the corners of slotted waveguide 152 as it is used in the antenna according to the invention. As Fig. 8 shows, is a first group of slots 16o inclined in a first direction, while a second group of slots 162, which cut in the front of the waveguide has a slope in the opposite direction. the Slits are regular in the narrow side forming the front of a wave conductor 152 cut so that they resonate at a frequency equal to the twice the wavelength spacing in the waveguide. In this way, in the case of resonance, all slots oscillate in phase and the beam is oriented perpendicular to the longitudinal direction of the waveguide. For the case of resonance, the slots 16o and 16 2 pure conductance values and add up, since the slots are shunted in the antenna storage area. At the resonance frequency the load | is a pure resistance and is equal to the sum of the conductance values of the slots.

In order to get the correct surface coverage, the waveguide is used energy is withdrawn from each of the slits when blasting. Due to this fact, the effective value of the slot increases with it the distance from the feed point for the waveguide, so that overall there is an effective conductance that is significantly greater than Is "1" and consequently leads to a large resistance mismatch occurring in the case of resonance. Because of this, the arrangement according to the invention slightly above the resonance

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frequency operated. The beam will therefore be one to two beam widths focused far from the broad side of the antenna. Under these conditions, a standing wave ratio is less than 1.2: 1 ensured. The antenna described above for a preferred embodiment operates in the Ka-band at 178 Wavelengths. For a further description of the theory of such corner slotted waveguide assemblies reference is made to the work "Antenna Engineering Handbook" by H. Jasek, 1961, McGraw Hill, Chapter 9.

The X / 4 plate polarizer 154 converts the horizontally polarized wave from the waveguide into a circularly polarized wave. The polarizer 154 is an X / 4 arrangement that includes a plurality of evenly spaced metallic strip dividers embedded in a foamed, low loss dielectric material (Ecco foam). The metal strip dividers are oriented at an angle of 45 ° with respect to the antenna polarization, so that they convert the linear polarization into a circular polarization. By using this method for circular polarization, an integrated cancellation ratio (ICR) of 17 dB can easily be achieved.

Although not shown in the drawing, in a preferred embodiment the antenna waveguide 152 is on returned a second path over the entire length of the antenna, to achieve a symmetrical loading of the same. The waveguide and the horn antenna generally consist

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in one made of aluminum and are rigidly connected to each other. Of the Shift motor which is used in the preferred embodiment of the invention under consideration is a brushless one DC switching motor with a permanent magnet as a rotor and a ring winding as a stator. The motor will swing for a movement of + _ 25 for a continuous output of 8 watts and for a peak torque of approx. 1.6 kg cm. A high pressure replacement bottle with Frigen 116 is located near the far end of the waveguide and leads the waveguide over a reducing valve Frigen adjusted to a predetermined pressure. A pressure gauge that fits on the bottle allows the test of the frigen store, and a similar arrangement is together provided with a supply valve at the end of the waveguide facing the load and allows the pressure to be measured in the Waveguides as well as draining the system after maintenance.

Fig. 9 shows in the form of a block diagram the circuit for the control the pivoting movement of the antenna 42. The transducer 44 is formed by a linear transformer which is connected to an output demodulator circuit 168 delivers a modulated 2 kHz signal. A reference voltage that is normally the 2kHz aircraft supply voltage is fed to the transducer 44 and also to a reference demodulator and control residual summing circuit 17o. These Circuit 17o compensates for changes in the amplitude of the aircraft supply voltage and supplies a multiplier circuit 17 2 a voltage of constant amplitude. The reference demodulator and control residual summing circuit 17o prevents the evaluation in this way of voltage changes in the aircraft supply voltage as changes in the antenna position.

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The output of the output demodulator circuit 16 8 is a direct current signal which slowly changes with the antenna swivel frequency or the sampling frequency changes, which is 2.5 Hz in the preferred embodiment. The output signal the output demodulator circuit 16 8 thus corresponds to the instantaneous position of the antenna 2o. At the output of the multiplier circuit 172 a signal is generated which corresponds to the antenna position and a 9o phase shifter 174 and an absolute value amplifier 176 is fed. The 90 ° phase shifter 174 shifts the sinusoidal output signal of the multiplier circuit 172 in such a way that their zero crossings correspond to the occurrence of peaks of the waveforms. One detector 17 8 for the positive zero crossings produces an indication of the positive amplitude peaks of the antenna position signal, while a detector 18o for the negative zero crossings an indication of the negative voltage spikes of the antenna position signal supplies.

The output of the detector 178 is applied to an input of a OR circuit 182 placed and also to the trigger input a voltage-dependent, monostable multivibrator 184 for pulse length modulation. The output of the detector 18o becomes also fed to an input of the OR circuit 182 and also to the trigger input of a voltage-dependent, monostable Multivibrators 186 for pulse length modulation. The multivibrator 184 is activated upon the occurrence of each positive spike in the antenna position signal triggered, while the multivibrator only occurs when the negative peaks of the antenna position signal occur is triggered.

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The output of the OR circuit 182 is a sampling and Hold amplifier 188 supplied. The absolute value amplifier 176 directs the antenna position signal from the multiplier circuit 172 and provides a positive output voltage that is a measure of both the left and right scanning tip positions of the antenna. This information is the Sample and hold amplifier 18 8 supplied, which then only generates a positive voltage that of the left and right peak positions corresponds to the antenna when the occurrence of a position spike has been detected by the OR circuit 182. These Voltage is applied to the multi vibrators 184 and 186. There the multivibrators 184 and 186 are triggered alternately by the detectors 178 and 18o, is triggered by the multivibrators alternately generates an output pulse of a monostable multivibrator, which the alternating left and right antenna position tips is equivalent to.

The pulse width of the multivibrator output signals is of the determined position of the antenna dependent. The pulsed output signals of the multivibrators are used in a driver matrix 188 ', which consist of a transistor driver or a driver circuit with controlled silicon rectifiers can. The pulsed output signals are then applied to the switch motor 42 to control the position of the antenna. One of the pulse outputs drives motor 42 clockwise while the other pulse output drives motor 42 counterclockwise drives. When the panning movement of the antenna begins to slow down, the pulse width of the output signal becomes

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nale of the multivibrators increased to drive the antenna to increase. If, on the other hand, the left and right end positions of the antenna begin to exceed certain limits, the Width of the pulse-shaped output signals of the multivibrators 184 and 186, so that the drive movement for the motor 42 is decreased.

Radar receiver

Fig. Io shows a block diagram of the radar receiver of the invention Systems. The radar signals received by the antenna are fed into the ferrite circulator 52, previously described was described, fed. To test the receiver, a load 2oo is attached to the circulator 52. The transmitter magnetron is also connected to the circulator 5 2. The circulator is operated as a duplexer to allow the use of a single Enable antenna. The signals coming from the transmitter are sampled via a coupler 2o2 and via a power monitor circuit 2o4 applied to an input of a NAND gate 2o6, as well as to the built-in test unit of the system.

The signals received by the antenna are passed through the circulator 52, which may be, for example, an R-641-LS circulator manufactured by Ferrotech, Inc. and is sold. The signals then reach a transmit / receive switch 2o8. The transmit / receive switch 2o8 can consist, for example, of an interrupter of type MA-3773,

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as manufactured and sold by Microwave Ass. A pre-ionization circuit 21o supplies the bias voltage for the transceiver switch 2o8, so that the switching tube a Has a tendency to breakdown and thus brings about signal isolation in a known manner. The received signals are also passed through a ferrite switch 212, which causes additional attenuation compared to the transmission pulses. The ferrite switch can for example be a switch of the type LTW-IoS, as manufactured and sold by the company Ferrotech, Inc. will. The PMT signal

is passed through a switch driver 214 which controls the actuation of the ferrite switch 212.

The receiver signals are passed through a signal mixer, which contains two oppositely polarized diodes 216 and 218. Between the diodes there is a resistor 22o, both ends of which are connected to two inputs of a NAND line 222. A Semiconductor oscillator 224, which is designed as a voltage-controlled oscillator, supplies a 50 mW signal with a frequency from 1.458 GHz to a power amplifier, which increases the power to about 1 watt. The signal then becomes one with the Factor 6 multiplying multiplier circuit supplied to the is preferably made in thin film technology. The resulting 2 50 mW signal with a frequency of 8.75 GHz becomes one supplied by a multiplier circuit multiplying by a factor of 4, which produces a final signal of Io mW with a frequency of 32.94 GHz _ + 150 MHz. This signal is sent via a Isolation circuit 226 passed and with the received signals

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mixed. The frequency applied to a linear amplifier 22 8 is an intermediate frequency of 60 MHz.

The intermediate frequency signal is amplified in linear amplifier 228, to which a post-echo attenuation signal is also applied to reduce receiver saturation as the target area decreases. The post-echo attenuation signal is generated by a generator 2 3o, which in turn is controlled by the PMT signal of the system. The amplified signals are then fed to a logarithmic post-amplifier 232 where they are given an 80 dB gain. A manually adjustable gain controller is connected to the amplifier 232. The amplifier ¹ 232 has a linear-logarithmic characteristic which is adapted to the dynamics of the display area of the system in order to ensure an optimal display of the radar target information. In a preferred embodiment, amplifier 232 has seven stages, each of which operates on low power signals. As the received signals get stronger, one of the stages will saturate one after the other, resulting in an output voltage that is a linear function of the input energy to the system.

The output of the amplifier 23 2 is connected to a video detector and amplifier 2 34, the output of which is connected to an emitter follower is formed. The detector 234 regulates the 60 MHz signal and works as an envelope rectifier to generate a Video voltage pulse. The amplifier 232 can also be used to de-cloud if desired by the operator. The development

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turbidity is used to break down targets with a large cross-section, such as airport buildings or residential areas, to achieve saturation to prevent the radar display. The video voltage pulses are described in detail later in a Manner applied to the display device of the system.

A power monitor coupler 2 36 detects the output from the magnetron transmitted signals and feeds them to a mixer for automatic sharpening, which has two oppositely polarized Contains diodes 238 and 24o. The output signal of the isolating stage 226 is also monitored by a coupler 242 and sent to the Mixer created for automatic sharpening. If that System is working correctly, the mixed signal should be at the intermediate frequency and is passed through a limiting amplifier 244 is applied to the autofocus circuit 246 /. The output of circuit 246 is applied to one input of NAND circuit 222. The mixer for automatic Focusing is also connected to two inputs of the NAND circuit 222. The circuit 246 for automatic Sharp tuning is via a movable switching arm 24 8 with the semiconductor oscillator 224 and a terminal 25o connectable. The terminal 25o is connected to a test resistor 252, whose the other end is at the reference potential.

The auto-sharpening circuit described above maintains frequency synchronization between the receiver and the transmitter. If the receiver is working properly, the resulting signal from the mixer should automatically

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automatic sharp tuning lie at the intermediate frequency. That mixed signal is applied to autofocus circuit 246 which includes a discriminator and a Contains reference frequency oscillator and serves to generate a direct current signal which the control of the semiconductor oscillator 224 serves. If it is possible, the semiconductor oscillator 224 to drive the desired frequency, the resulting signal is applied to NAND circuits 222 and 2o6 in order to to turn on a fault indicator light 254 located on the aircraft instrument panel. Through the performance monitor circuit 2o4 the presence of a minimum peak output voltage of the transmitter is also monitored and in the event that the output power falls below a specified minimum value, the error indicator lamp 2 54 is switched on.

The presence of the bias voltage for the mixer crystal is also detected by the NANJJ circuit 222 and if it fails The error indicator lamp 254 is turned on after the bias. The lighting of the error indicator light 2 54 indicates that a of the conditions has dropped below a minimum value specified in the design of the system, but this is not necessarily yet the case means a complete failure of the radar system. Li; must be left to the judgment of the operator remain to decide when the information provided by the system has deteriorated to the point that it is completely unusable. To the operator such a decision to enable, the movable switching arm 24 8 can be brought by hand into the position in which the automatic arming

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Voting can be checked, and a movable switching arm 256 can be brought into a position in which the output of the linear amplifier 228 is connected to a calibration mark oscillator 258.

The calibration mark oscillator 25 8 generates a series of intermediate frequency pulses, which have a predetermined distance from each other. The pulses are transmitted via the logarithmic amplifier 2 fed to the viewing device. Six horizontal lines are displayed on the radar screen as well as a vertical line, their position corresponds to the airline of the aircraft. This is achieved by simulating a height of 50 feet in the display. The calibration mark oscillator 258 is excited by a damped transmission pulse, so that it generates a pulse train of 60 HKz pulses, which are 2,000 feet away within the radar range and which decrease in amplitude with increasing range. the Pulses generated by the calibration mark oscillator 2 58 are displayed on the screen as horizontal lines giving a Reference to the correct operation of the antenna drive circuit, the resolver and the display circuit.

The amplitude of the pulses fed to the logarithmic amplifier 232 is selected so that six horizontal lines are generated on the screen which, at an altitude of 500 feet, correspond to a ¹ Kadar range of 2,000, 4,000, 8,000, 10,000 and 12,000 feet. The seventh and all other pulses of the calibration mark oscillator 25 8 are below the response threshold of the system and are therefore not shown. the

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Vl

Line generation with the help of the egg clunar oscillator supplies a useful indication of the correct setting of the gain control for the radar receiver and in the event that If fewer than six lines are displayed during the test, the receiver sensitivity is below that during the Operation required minimum. The position of the vertical calibration line, which appears on the screen during the test is determined by the resolver for the antenna position. the The position of the vertical calibration line in the horizontal direction with respect to the center line is a measure of the linearity and accuracy the liildröhrenablenkschaltungen for the electron beam.

A more detailed description of the function of a radar receiver is to be found in the work "Introduction to Radar Systems" by Merrill I. Skolnek, published in 1962 by McGraw-Hill Verlag im 8th chapter.

Radar transmitter

11 shows a block diagram of a radar transmitter for a device according to the invention System. The system is supplied by the usual Moo Hz aircraft supply, namely via a chase filter 2 8o, which is the high frequency components from aircraft supply excitation filters out. A 3-phase relay switch 2 82 switches the Moo Hz signal to a diode transformer 2 84 by. An overload protection circuit? 86 prevents overloading of the system and a magnetron heating circuit provides 2,888

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Power to the heating wire of the magnetron. Via a transformer 29o, a heating current is also fed to a thyratron 3o2.

A 3-phase bridge 292 supplies a rectified voltage via an L-element filter 29M. a charging choke 296. A load resistor 298 provides discharge protection for the L-element filter 294 when the system is switched off. The charging choke 29β contains inductances which present a high impedance load to the system. The voltage is applied to the thyratron 3o2 of the transmitter via an inverting charging circuit 3oo with diodes. A trigger circuit 3o4 supplies trigger pulses to the grid of the thyratron 3o2. The output signal of the thyratron 3o2 is fed to a pulse-forming network 3o6 which emits pulses when the thyratron 3o2 ignites. The pulses from the network 3o6 are applied to the magnetron 3Io via a pulse transformer 3o8. The modulator according to the invention is filled with oil in order to prevent a voltage breakdown at great heights, so that it fulfills the negative pressure test conditions required by the FAA regulations. A number of Ka-band magnetrons are commercially available; according to the invention, however, a tunable tube of the type L-456 ^l i, which is manufactured and sold by Litton Industries and which is modified so that it delivers a peak power of 80 kW, is preferred. The energy for the magnetron 31o is supplied by a filament transformer 312. The output of the magnetron 31o is applied to the circulator 52.

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The synchronizing circuit 5 8 supplies the PMT signal for the time Control the system as described above.

The synchronization circuit delivers during operation of the radar transmitter 58 a PMT signal to the trigger circuit 3o4, which delays the PMT signal and the trigger signal for the thyratron 3o2 delivers. The thyratron 3o2 normally has a high impedance and the pulse-forming network 3o6, which is preferably contains a chain of LC networks, is charged to the anode voltage applied to the thyratron 3o2. if the thyratron ignites, the pulse-forming network 3o6 discharges via the pulse transformer 3o8, which steps up the voltage and provides a high control voltage for the magnetron 31o. From the pulse-forming network 3o6. Is a signal with a pulse width of 4o ns, which is applied to the magnetron 31o. The inverting charging circuit 3oo forms a return path for the energy resulting from the Mismatch between the pulse-forming network and the pulse transformer during discharge not to the magnetron is transmitted. The modulator is protected by the overload protection circuit 2 86 against overloads caused by excessive Mains voltage fluctuations due to arcing in the Earth the magnetron or caused by interruptions in the circuit in the magnetron. When an overload occurs, the 3-phase energy for the high voltage supply of the modulator interrupted.

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A more detailed description of the operation of radar transmitters can be found can be found in Chapter 6 of the aforementioned work by Skolnek.

Tilt generator system

Referring to Figure 12, there is shown a block diagram of the relaxation generator system. The radar altitude display and the barometric altitude display from the aircraft's altitude measuring devices are fed to a limiting filter 35o, which is constructed in such a way that the system according to the invention does not work at altitudes below 50 feet. The limiting filter 35o also has the tendency to smooth height signals so that the measurement results on towers, trees or the like are not evaluated. The filtered signals are then fed to three wave formers 352, 354 and 356. The wave shaper 352, which will be explained in more detail below, transforms the input waveform in such a way that an output signal results _3, the voltage of which changes in relation to the level in the manner shown in the drawing.

This voltage is then applied to an RC circuit that consists of a resistor 358 and a capacitor 3Go. A diode clamping circuit 36 2 controls the charging of the RC circuit. The output of the waveguide. 354 is attached to an FC circuit applied from a resistor 364 and a capacitor 36G, their charging process from a transistor clamping circuit 36 8 is controlled. In a similar way, the output voltage

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voltage of the wave shaper 3 56 to a KC circuit from a resistor and a capacitor 37 2 is applied, the capacitor 372 having a transistor clamping circuit 3 74 connected in parallel is. Each of the output voltages of the waveformers 352, 354 and 356 is also fed to a summing and subtracting circuit 37G. The sum of the three output voltages is subtracted from a reference voltage, which is transmitted via an input mine 37 8 is fed and the opposite to a maximum elevation angle dor the horizontal of 12.1. The output voltage of the summing and subtracting circuit 376 is thus a Measure of the voltage that is required to obtain the sumr.e of the Wave shapers 352, 354 and 356 to a maximum elevation angle from 12.1 to bring. The output of the suiming and Subtraction circuit 376 is made up of a KC circuit. resistance 3 8o and a capacitor 3 82 supplied. A diode clamping circuit 3 84 is connected in parallel to the capacitor 3 82.

An important aspect of the present invention is the fact that the time constants of the various RC circuits of the Kippgeneratox- "s are changed. For example, the value of capacitor 372 is equal to 125 times the value of capacitor 36o, while the capacitance of capacitor 366 is 25 times that of Capacity of the capacitor is 36o. The capacitance of the capacitor 382 is equal to 5 times the capacitance of the capacitor 3Go.

The exponential voltages appearing at the capacitors 36o, 366, 372 and 382 (with the clamping circuits disabled) are all sent to the input of a Suinmier amplifier 39o

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whose output signal is applied to a driver amplifier 394 via fine relay selection control 392. The sum of the exponential voltages that are generated when the RC networks can charge themselves to the voltage supplied to them by the associated waveforms without being hindered by the clamping circuits, changes approximately in accordance with the ratio of aircraft altitude to time or radar range . The output signal of the driver amplifier 3 9 4 is used to control the vertical line amplifier of the radar picture tube. In a manner that will be described in more detail below, this amplifier delivers a non-linear signal which leads to a lifelike, perspective representation of the runway approached. The limited and filtered altitude signal is also fed to a voltage controlled delay circuit 398. The output signal of the ¹ delay circuit 398 controls the time at which an inono-

Distraction

stable multivibrator 4oo with a / process corresponding Pulse width is triggered, and the output signal of this multivibrator 4oo is used to control each of the sound circuits 362, 368, 374 and 384.

The PMT signal is also sent to the delay circuit 39 8 and also to the generator 402 for generating the symbol horizon and scan marks. The control of the generator 4o2 is used by the horizontal tilt signal applied to it. To the delay time determined by the delay circuit 39 8 the monostable multivibrator 4oo separates the clamping circuits 3G2, 368, 374 and 384 from the RC circuits, so that these

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begin to charge themselves to the voltage levels assigned to them according to their various time constants Waveformers are offered. The sum of the from the KC circuits The generated voltages are then a measure of the relationship between aircraft altitude and radar range. The one from the delay circuit 39 8 is linearly proportional to the aircraft altitude. At the end of the pulse duration of the monostable Multivibrators 4oo put the clamping circuits and capacitors back to reference potential.

After disconnecting the various clamping circuits, the voltages generated by the KC circuits are sent to the summing amplifier to control the vertical line amplifier of the display device. The modulated antenna position signal, which is supplied by the encoder scanning the antenna position is fed to an antenna demodulator circuit 4o6, which supplies a signal to a cosine generator 408 and to an amplifier 41o which indicates the antenna position. A signal is sent to the amplifier 41o as a further input signal from a heading demodulator circuit 412 is applied. This receives input signals from the one already described above Control housing and from the gyrocompass of the aircraft and generates a signal which is a hatred for stabilization of heading is.

The output of the amplifier 41o is applied to a selector relay 414. V / enn at this selector relay 414 the B-scanning or the lifelike Sampling is set, the output of the

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3?

Amplifier 41o fed to a line driver 416, the output of which to drive the horizontal deflection is connected to the radar picture tube via a coaxial cable when it is in B mode works or creates a lifelike, perspective representation. If on the selector relay 411 the all-round view or PPI display is selected, the output of the cosine generator 4q8, which corresponds to the angle θ or the antenna position, via an integration amplifier 418 and via an amplifier 42o for control to the horizontal line driver 416 created.

The output of the heading demodulator circuit 412 becomes the amplifier 41o for modifying the horizontal scanning voltage fed. The visual display is then compensated so that if the aircraft changes course slightly, the runway is removed remains in essentially the same location to prevent the runway from moving during a rough approach is carried out.

Another output signal of the cosine generator 408, which corresponds to the cos θ of the antenna position, is sent to a selection circuit 424 is applied to select the PPI or the B representation, and the output of this selection circuit 424 becomes via an integration amplifier 426 and an amplifier 428 applied to the relay selector control 39 2. The amplitude of the vertical B breakover voltage can be regulated by changing the resistance 4 3o at the selection circuit 42 4. The output signal of the amplifier 428 is transmitted to the driver amplifier 394 via the relay selection control 392 in the case of B or PPI operation

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and is used to control the vertical deflection of the radar picture tube.

A relay selection circuit 436 can be operated in four different operating modes as a function of four Bei'eichs input signals, and its output is connected to a circuit 438 which is used to delay the PPI and B display. In the operating mode in which the "automatic range" input signal is fed to the circuit 436, an 83 second deflection circuit is used in the delay circuit 438. This deflection changes the PPI, or B-delay time to an extent which corresponds to the speed at which depart ^1, the aircraft would approach the runway normally. The circuit 4 38 is connected to a PPI or B deflection width circuit 44 o which provides a signal for the integrator reset circuit 4 42, which resets the integration amplifier 426. The PMT signal is applied to the S-L input of a flip-flop circuit 446, and the deflection width circuit 44o is connected to the R input of the flip-flop circuit 446.

To an intensity compensation circuit 4 5o, which is a line driver 452 to control the pre-brightness control of the picture tube controls, several input signals are applied. That PMT signal is applied to the intensity compensation circuit 45o and also input signals from the deflection circles to indicate the healing control duration and the deflection of the vertical deflection signal to be determined for the lifelike representation. The derivation of the vertical deflection voltage for the lifelike presentation

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Position is added to a pulse during the time that is desired to control the light of the tube. The amplitude of the Derivation of the vertical deflection signal for the lifelike display changes as a function of altitude and time, so that the signals corresponding to a low altitude at the beginning of the deflection are supplied with greater intensity than those corresponding to a greater height.

A roll demodulator circuit 45 determines the gyrocompass of the aircraft is its movement around the roll axis. The output of the demodulator 454 becomes a multiplying unit 456 for four quadrants, which provides an input signal for the summing amplifier 39o. The horizontal deflection signal for the lifelike representation is also fed to the multiplication unit 456 and is used in this with the Roll angle multiplied and then added to the vertical scanning signal. In this way the circuit determines the rotation of the aircraft and accordingly rotates the image of the runway displayed on the radar screen to the lifelike one Support illustration.

When the system is working in B mode, the selector switches

gen 392 and 414 in the position corresponding to the B operation brought, with the help of the operating a ^ ten selector switch on Instrument panel of the aircraft. The. modulated antenna position is thus via the antenna demodulator circuit 4o6 and the Amplifier 4lo is applied to the horizontal line driver 416. This means that the horizontal deflection of the display tube of the antenna

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• rt

Pan proportional. The vertical deflection, is used for the B mode is set at circuit 44o and via the integration amplifier 426 and the amplifier 428 to the vertical line amplifier 394 is supplied, so that a linear ramp function is generated which increases as a function of time and is used to control the vertical deflection of the picture tube. The end of the distraction is indicated by the circle at each distraction period 44o determined. The resulting screen image on the radar tube corresponds to the usual B display.

If a delayed B display is selected with the help of the selector relay a section of the recorded area is displayed on the radar screen. It works the circuit as described above except that the delay circuit 438 operates to take effect vertical B deflection for the time interval selected on relay selection circuit 436 is prevented.

The automatic range selection mode can also be used can be set at the relay selection circuit 436, with the 83 second deflection of the delay circuit 438 switched on will. This operating mode changes the time delay, with which the vertical deflection is initiated and thus compensates the speed of the aircraft, so that the found The runway remains essentially in the same place on the picture tube, eliminating the problems of identification and detection the position of the runway on the radar screen. During the approach of the aircraft the runway becomes larger, but remains visible on the picture tube, so that the

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Switching of the areas for the image display can be omitted.

In the PPI mode, the relay selection control 392 is in the PPI position switched. The vertical line driver 394 becomes thus driven by a positive ramp signal from the cosine generator 408, the amplitude of which is proportional to the cosine of the The antenna signal is supplied to the antenna demodulator circuit 406. The horizontal line driver 416 becomes driven by the cosine generator 4o8 via the integration amplifier 418 and the amplifier 42o, and that accordingly a range approximation multiplied by the sine of the azimuth angle, which for the present system can be approximated by the area multiplied by the azimuth angle. As already As mentioned at the beginning, the B display, the delayed display and the PPI display are carried out in the usual way and are not intended to be discussed in further detail.

In the case of the mode of operation according to the invention of true-to-life representation the selector switches are brought into the correct position and the radar altitude signals or the barometric sound signals are supplied to the limiting filter 35o. The filtered and clipped signal is applied to waveform shapers 352, 354 at the same time and 356, in which voltages are generated which are dependent on the level in the manner shown. These tensions are applied to capacitors 36o, 366 and 372 and clamping circuits through resistors 358, 364 and 37o. Additionally becomes a voltage which is the difference between an elevation angle between 12.1 and the sum of the output signals of the

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Wave shaper corresponds to the RC circuit from the resistor 38o and the capacitor 382 as well as to the diode clamping circuit 384 applied. After separating the various terminal connections The RC circuits begin according to their respective Charge time constants. The summing amplifier 3 9o thus generates a vertical drive signal which is a non-linear function is, which obeys approximately the following equation:

where ß = elevation angle, h = aircraft height and

r = current target area of the radar signals.

A vertical deflection signal for the Baldröhre corresponding to the non-linear equation (1) leads to a runway display on the screen that is directly related to the realistic, corresponds perspective view of the runway from the aircraft. In other words, it becomes the runway served shown with a straight center line and straight side lines, which converge towards the rear of the runway, as is the case with a true-to-life perspective. That Bild thus not only helps your pilot with the exact determination lateral deviation of the aircraft from the runway and from the touchdown point on the runway, but also in finding a smooth transition from pictorial representation the runway for an actual view of the runway

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the cockpit window during landing. As above mentioned, the known representations, such as the PPI and the B representation, provide images that are distorted in relation to reality an approached runway.

Figures 13 to 16 are now intended to provide an understanding of the mode of operation support the lifelike image according to the present invention. An examination of the factors that make the affect perspective vision has shown that that The human eye works essentially in a spherical coordinate system, one of the reasons for depth perception with one-eyed vision lies in the fact that oblique angles are perceived. As a result, the human Eye perceives parallel lines that tend to converge at infinity, although the angle between the parallel lines is almost zero. The radar system according to the invention must therefore depict straight lines in space as straight lines on the radar screen and also a linear perspective supply, in which parallel lines converge at infinity seem.

In the method according to the invention for lifelike imaging the azimuth apex angle of the system and the elevation angle are determined ß is produced synthetically. For this synthetic generation of ß it is assumed that the terrain is below the Airplane is a horizontal plane. If one now looks at FIG. 13, one recognizes that the angle β is given by the following equation can be represented:

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-1
(2) & = sin

R _s Co., tT
where R = slope distance to one

Point of the terrain h = aircraft altitude and OC = azimuth apex angle

If the altitude is known, ß can be used for targets along the aircraft course (OC = 0) can be calculated, assuming that the following relationship applies to flat terrain:

(3) R (Ü, t) = Kt

where K = constant for distance units

per unit of time and t = time.

If one now looks at FIG. 14, one recognizes that a long, straight target, which lies transversely to the aircraft course, is used as a target L is recognized. It is now desirable that the target L in the true-to-life representation according to the invention as a horizontal Line appears. Normally, however, if there is no correction of the breakover voltages applied to the radar picture tube takes place, the image of the target L have a certain curvature. For example, let Ls be assumed to be the constant K was chosen to get a proper mapping of targets along the baseline for any fixed elevation. Target

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le along the curved line L will appear as a straight line for some azimuth angles OC to the side of the aircraft course in a conventional radar image, as shown in FIG. This is the natural result of the fact that equation (2)
for ß does not contain an expression that is a function of CX. is and also a consequence of the fact that R and h are not with

cc change. Thus, the constant location of ß describes an eogen on the hypothetically flat surface of the earth, which is a constant Slope distance R corresponds to.

It is thus assumed that a vertical 'Kip;
according to the following equation:

Equation (2) a vertical breakover voltage ß is generated, and

(4) β = K sin ^-1 ~
ds _Kt

where K ⁼ image scale factor in volts per inch

and degree.

Correct mapping thus takes place along the course of the aircraft when the terrain is flat. However, points of target L that are to the side of the course line (ex = O) are shown in the figure not shown as a straight line.

If one looks at FIG. 16, one recognizes that the oblique distance to points of the target L can be derived in a simple manner from the oblique distance R (Q, t), namely in a simple manner
following equation:

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(5) R <ot, t> =

R _s (O, t)

S COS CX

COS OC

if the target L is the course line intersects at time t, then applies;

^R s ^(Ü ' ^t O ^{) = Kt} O' ^and

Kt ₀

(CX, t ₀ ) = _-

cosoc

The elevation angle along the course line at the intersection of the Objective L is then:

- Λ Vt

(6) ß "= sin

For other points of the target L, the angle β is a function from ex. , nänilich:

(7) ß (oC) = sin

Kt

. -1 h cos ex. i

ι η ^

Equation (7) explains the graphical representation shown in Fig. Ib is shown.

To link the L line on the screen, the Breakover voltages for the picture tube ideally according to a function modified by oc. Assume that the vertical Breakover voltage obeys the following equation:

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(8) β = K sin -

α s

Kt cos OC

then t changes for points along the line L according to the following Equation:

2, where

(9) t = t cc (Ιο) ^ß d = cos sin K
S.

^Kt ü

thus L would now appear in the figure as a horizontal line (ß “).

In order to keep the costs and the technical effort for the illustration low to hold, it will now be generally desirable to approximate the equation developed above for the vertical deflection (β) 8. Obtain.

Two obvious approximations can be considered for this will:

sin xx (for small values of x), and cos y = * 1 (for small values of y).

The waveform for the vertical deflection voltage can therefore be approximated by the following functions:

K _sh
(11) ^ß _d t =, or

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(12) ß _d , =

Kr
where r = radar target distance.

FIG. 17 shows a graphical representation of β according to equation (12) over the distance, specifically for various Ilughheights. In the system according to the invention, a maximum Elevation angle ß of 12.1 used. The non-linear character of equation (12) can be clearly seen in FIG. For a height of 50 feet, corresponding to curve 50, the angle of elevation falls ß very quickly at short distances. As is clear from the curve 5o2, the elevation angle β begins according to Equation (12) at an altitude of 100 feet to fall off only at the same distance as that for curve 500 is applicable. Similarly, curve 504 shows that for an altitude of 500 feet, there is no decrease in the elevation angle β for a distance which is greater than for curves 500 and 5o2.

If one now looks at the line intersecting the curves 5oo, 5o2 and 5ο ¹ + at the value β = 12.1, one recognizes that the distance delay between the various curves is a linear function of the height. This linear delay is simulated in the system according to the invention by the voltage-controlled delay circuit 398, which controls the pulse width or the deflection signal width of the monostable multivibrator 4oo for the actuation of the various clamping circuits according to the invention. The marginal distance of the various curves in Fig. 7

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is, based on the distance, by the output pulse of the irionostable Multivibrators 4oo determined.

Fig. 18 shows in more detail the various waveforms, which are simulated by waveformers 352, 354 and 356 in FIG. The waveform 5o6 is a function that is approximated by the wave shaper 352, and it can be seen that iä - plotted in degrees of elevation - with increasing flight altitude falls off quickly. Thus, the voltage supplied by the wave shaper 352 has the greatest impact on the vertical Tipping voltage at lower altitudes, i.e. when the aircraft begins to land. Waveform 5o8 shows the function approximated by wave shaper 354, and it can be seen that the output voltage of the wave former 3 54 with the flight altitude rises linearly up to a value of 42 5 feet and then at higher altitudes with reduced speed increases. According to the invention, the voltage generated by the wave shaper 354 therefore has a primarily at greater heights Influence on the vertical deflection voltage.

Waveform 51o is a function created by the wave shaper 356 is approximated, and it can be seen that the output voltage generated by wave shaper 356 is primarily at higher altitudes of the aircraft has an influence on the vertical deflection voltage. Waveform 512 represents the output signal of summing and subtracting circuit 3 76 and shows a voltage that is required to be the sum of the output signals to keep all waveformers equal to a voltage which corresponds to an elevation angle <el ß of 12.1. You can see that

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the output of the summing and subtracting circuit 376 primarily affects altitudes between 100 and Hoo feet is.

The effect of the waveforms shown in Fig. 18 produced by the Waveformers 352, 354, 356 and 376 in the related to 12, is that the non-linear curves shown in FIG. 17 are generated by the " inventive system are approximated.

Figures 19a to 19d show four representations of a runway at different heights and distances, as they are shown on the radar screen of the system according to the invention. In a preferred embodiment of the invention, a radar picture tube is used in the form of a direct view storage tube with a diameter of approximately 12.5 cm, so that a usable image area of approximately 1 m edge length results. Only the useful part of the screen is shown in FIGS. 19a to d, and it goes without saying that the drawing only shows approximations of the actual image. For example, in a real radar image i runway is generally represented as a dark target in a bright field.

The horizontal scale of the radar picture tube, starting from the center point, is calibrated to + 15 to the right and - 15 to the left. The vertical scale of the picture tube is, starting from 0, on the horizon , which is represented by the line 513, calibrated down to 15 below the horizon. A dotted, horizontal one Line 514 represents the glide slope at 2.5 below the horizon

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to reveal the touchdown point on the runway. During the landing approach, which is shown in Figures 19a to d, the glide path of the aircraft is 2.5, and the drift angle, the course error and the touchdown deviation are both zero.

19a shows a 150 foot wide runway 516 from a distance 2 miles from the touchdown point and at an altitude of 53o.9 feet. The practical use of the system according to the invention has shown that the image of runway 516 on the screen is the same as the image the pilot sees when looking through the cockpit window looks amazingly similar. 19b shows runway 516 from a distance of one mile from touchdown point and for an altitude of 265.5 feet. 19c shows an image of the runway 516 from an even smaller distance, namely from a distance of 0.5 miles at an altitude of 132.7 feet. the dotted line 514 clearly shows the touchdown point on the runway. 19d shows an image of runway 516 from a distance from 0.19 miles from the touchdown point and from an altitude of 50.1 feet.

From all of the views of a runway shown in FIGS. 19a to d it can be seen that the illustration according to the invention corresponds directly to the natural perspective that results from the aircraft when looking at the runway. In particular as shown in FIG. 19d, the optical image of a runway is shown, ' which has a straight leading edge 518 and straight side edges 52o and 522 which point towards the rear end of the runway 524 converge, as in a realistic one Perspective is the case.

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It goes without saying that in the event that the aircraft is offset to the side of the runway during the approach, also the runway will be offset laterally from the vertical center line of the radar picture tube and that the shape The runway also changes accordingly to the natural view of the runway as seen from the aircraft with the given lateral deviation results to simulate. When the aircraft approaches the runway at a lead angle, Furthermore, the image of the runway will clearly show the pilot that the approach is not optimal. In addition, will If the aircraft rolls undesirably, the screen shows the pilot that the runway is at a roll angle corresponding angle is rotated. It is also understood that the upper part of the circular radar screen, i.e. the Part above the horizontal line 513, as a result of the control of the deflection voltages of the radar picture tube by the device shown in FIG shown generator 4o2 for symbol, horizon and distance marks will represent the sky. The distance marks are on the radar picture tube to the right of the ones shown in FIGS. 19a to d are displayed so that the pilot receives information about the distance. These distance marks are i generated by the generator Ho2 in a manner as described above has been described. A suitable distance tracking system for the supply of distance signals to the generator Uo2 is for example in an earlier application (file number ...) described by the applicant.

Fig. 2o shows schematically, but going in more detail, the

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Wave shaper to generate the waveforms that are used to correct the non-linear vertical deflection of the radar picture tube steer. FIG. 2o shows, in more detail, the structure of the waveform shapers 35o bis in the block diagram according to FIG. 12 356 and electrical circuits referred to as summing and subtracting circuit 376, respectively. An altitude signal that indicates the altitude of the Corresponds to aircraft, is applied to a terminal 55o and is fed to one input of an operational amplifier 552. The signal is then sent through a filter assembly 554 for filtering.

Between the input and output of the operational amplifier 552 lie a zener diode 556 and other diodes to limit signals corresponding to an altitude of 50 feet or less. The limited signal is applied to the input of an amplifier 558. The limited altitude signal also serves as an input for an amplifier 56o. Diodes and other switching elements connected to amplifier 56o limit those from it processed altitude signals that are below a maximum effective altitude of 600 feet. The output signals of the fe amplifier 56o are applied to a summing point 562 where they can be combined with the output signals of amplifier 552. A filter circuit 564 is arranged parallel to the amplifier 55 8, which filters the amplitude-limited signal.

The signal is then fed to the inputs of amplifiers 56 6, 56 8 and 57o simultaneously. The limited and filtered signal is also connected to the inputs of amplifiers via a line 572

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574 and 576 supplied. A positive voltage is applied to an input cycle 578, which is applied to the inputs of the amplifiers 574 and 576 via resistor networks and added there with the other input signals fed to them. Additional circuit parts and in particular diodes 5 8o and 5 82 ensure that the amplifiers 574 and 576 serve as half-wave rectifiers. The rectified output signals of the two g circuits are combined at a summing point 584 and fed to the input of an amplifier 586. An adjustable resistor network 58 8 allows the initial voltage to be set for the circuits. The two half-wave rectifiers lead to dead zones when the circuit is in operation, so that their signal outputs do not rise above zero until a specified input voltage level is applied to them. The amplifier 586 including the associated circuit parts is linear only up to a voltage of zero volts and only passes negative signals on to the input of an amplifier 59o. The output signal of the amplifier 59 ° is therefore a voltage which is relatively high for input signals at the terminal 55o, corresponding to a low level, the amplitude of which, however, falls off sharply when signals are applied%, corresponding to a greater height. The output signal of amplifier 59o thus corresponds to waveform 5o6 in FIG. 18.

The output of amplifier 558 is sent to amplifier 56 applied, which is designed as a linear amplifying inverter, and whose output signal is a positive voltage. The altitude signal is also applied to the amplifier 57o due to

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of the diodes connected to it like an ideal half-wave rectifier works and its output signal is clamped by a negative voltage. In other words, that remains Output voltage to zero volts until the input voltage reaches a predetermined threshold. When the input voltage exceeds the exceeds predetermined threshold, a negative is on line 59 2 Output signal generated which tends to cancel the voltage at the input of amplifier 56 8. The so resulting waveform is fed to an amplifier 59 4, the generates an output signal corresponding to waveform 508 in FIG.

The limited, unfiltered altitude signals are also sent to the Amplifier 566 is applied, which generates a positive ramp voltage which increases with increasing height. The output signal of the amplifier 56 6 thus corresponds in its shape to the waveform 51o in FIG. 18.

The output signals of amplifiers 566, 59o and 594 are applied to a summing point 598. Is connected to a resistor network a positive voltage is applied in order to apply a reference voltage to the summing point 59 8 via a resistor 599. The above Voltage applied to resistor 599 corresponds to a maximum elevation angle of 12.1. The resulting voltage signal is applied to amplifier 6oo which then produces an output voltage whose shape corresponds to waveform 512 in FIG

Contains in a preferred embodiment of the invention

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Each of the amplifiers shown in FIG. 2o is an integrated semiconductor amplifier of the type SN 527o9, which is manufactured by Texas Instruments Incorporated is manufactured and sold.

In FIG. 21, the voltage-controlled delay circuit 398 and the monostable multivibrator 4oo, which have already been discussed above in connection with FIG. 12, are shown in more detail in a schematic manner. The PMT- d signal is fed to a terminal 6ol and arrives from there to an input of a NAND circuit 6o2, this input being connected to the reference potential via a diode. The output signal of the NAND circuit 6o2 is applied to one input of a NAND circuit 6o4, at the other input of which the output of a NAND circuit 606 is applied. The NAND circuits 6o2, 6o4 and 6o6 operate as an RS flip-flop, the output signal of which is applied to the base of a transistor 61o via a line 6o8. The base of a transistor 612 is connected to the collector of the transistor 6Io via a resistor and the collector of the transistor 612 is connected on the one hand to the reference potential via a capacitor and a Zener diode and on the other hand to an input of a comparator circuit 614. "

The collector of transistor 612 is also connected to the collector of a transistor 616. That of the transistors 61o, The output signal generated 612 and 616 is a ramp function that is applied to the comparator circuit 614. This ramp function is compared by the comparator circuit with an amplified altitude signal which is applied to a terminal 6 2o the second input of the comparator circuit via a

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stronger 622 and a line 624 is supplied. The output signal of the comparator circuit 614 is applied to one input of a NAND circuit 626, at the second input of which the PMT signal is applied. The output signal of the NAND circuit 626 controls the function of a NAND circuit 628 as a function of the PMT signal. The output signal of the NAND circuit 62 8 is used to control the monostable multivibrator ¹ Oo, which was described above in connection with FIG. 12.

The monostable multivibrator 4oo thus generates an output signal at the base of a transistor 6 3o, at the collector of which a signal then occurs, which the clamping circuits in Fig. 12 actuated. This signal is referred to as the brightness control signal for lifelike imaging. The output signal of the Multivibrators 4oo is also applied to the inputs of NAND circuits 6 34 and 6 36 via a line 6 32. The exits the NAND circuits 634 and 636 are connected to a NAND circuit 638, the output of which is applied to the inputs of the NAND circuits 6 34 and 636 is returned. The NAND circuits thus work as a digital differentiating circuit. The output signal this differentiating circuit is applied to an input of the NAND circuit 606 via a line 6 4o. The rear flank of the pulse generated by the monostable multivibrator 4oo is thus determined by the differentiating circuit and the resulting output of the differentiating circuit represents the RS- consisting of the NAND circuits 6o2 to 606. Flip-flop back. When the flip-flop is set, the Ramp generation circuit the generation of a linear Ramperi-

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function is initiated and the ramp voltage is used by the comparator circuit 614 compared with the altitude signal. If the ramp voltage exceeds the height voltage, it is the desired one The delay time has expired and the multivibrator Uoo is triggered to generate the brightness control signal for the lifelike image.

FIG. 22 shows schematically, but in more detail, the A KC memory circuits j, the clamping circuits and the summing amplifier 39o, which have already been discussed above in connection with FIG. The storage capacitor 382 and the clamping diode 3 84 have been omitted to clarify the illustration.

The light control signal generated by the circuit shown in FIG is applied to terminals 7oo and 7o2. The light control signal goes from terminal 7o2 to the base of a transistor 7OU, whose collector is coupled to the base of a transistor 706. The emitter of transistor 706 is through a zener diode and a capacitor coupled to the emitter of a transistor 708. The base of the transistor 7o8 is via an RC circuit Ί coupled to the collector of transistor 704. The collector of the transistor 7o6 is connected to the base via a resistor 71o of a transistor 712. The collector of the transistor 712 is connected via a diode 714 to an input terminal of a diode bridge 716.

The collector of the transistor 708 is connected via a diode 718

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an opposite connection of the diode bridge 716. The diode bridge 716 corresponds directly to the diode clamping circuit 36 2 in FIG. 12. The waveform 5o6 described with reference to FIG and which was developed with the aid of the circuit shown in FIG. 2o is applied to an input terminal 72o and charges an RC memory circuit made up of capacitors 722 and resistors 724 and 726 when the clamp circuit is disconnected. When the bridge 716 is disconnected, the voltage across the Capacitors are applied to a resistor 7 3o via a line 72 8. The resistor 7 3o is connected to the base of a transistor 732 connected.

The light control signal for lifelike imaging is also applied from terminal 7oo to the base of a transistor 736. The light control signal is then applied to the base of a transistor 74o via the collector of this transistor and a diode 738. The collector of transistor 74o is connected to the base of a transistor clamping circuit 742 and also to the base a clamping transistor 744. The transistor 742 corresponds directly to the transistor clamping circuit 374 in FIG. 12 and the transistor 744 corresponds directly to the transistor clamping circuit 368 in FIG. 12. The circuit shown in FIG. 2o generated waveform 51o is applied to an input terminal 478 and charges an RC memory circuit which is a capacitor 75o and resistors 752 and 754 after the light control signal is applied to transistor 742. the Voltage across capacitor 75o is -7 5 8 through a resistor applied to the base of transistor 732.

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The waveform 5o8 derived with the aid of the circuit shown in FIG. 2o is applied to a terminal 76o and charges a RC memory circuit with a capacitor 76 2 and VJi of the stands 764 and 766 when transistor clamping circuit 744 is disconnected. The voltage across the capacitor is via a line 77o is applied to a resistor 772 which is connected to the base of transistor 732.

The voltage that the fourth, not shown, RC memory circuit charges, is at terminal 7 8o and via a transistor 7 82 created. A roll signal is applied to the base of transistor 732 at terminal 7 84 through a resistor in the manner as previously described in connection with FIG was to ensure the correct orientation of the runway display on the picture tube with regard to the roll axis.

As mentioned above, the different time constants of the four RC circuits of the relaxation oscillator are chosen so located that provides a sweep voltage that approximates an inverse Zeitfunk- i tion. In addition, the output voltages change directly with height, so that a vertical deflection signal is generated which corresponds to equation (12).

The emitter of transistor 732 is connected to the base of a transistor 39o are connected and the collectors of transistors 732 and 79o are connected together, "so these two transistors form a Darlington pair. In a similar way

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the transistors 79 2 and 79 4 are connected to a Darlington circuit and form a summing amplifier for the non-linear signals. To the emitters of the opposite Darlington circuits, a transistor 79G a negative bias is applied.

The collectors of transistors 732, 79o, 792 and 794 are coupled to the base and collector of a transistor 8oo. The collector of transistor 79o is directly coupled to the base of a transistor 8o2. The emitters of the transistors 8oo and 8o2 are coupled via resistors to the collector of a transistor 8o4, the base and emitter of which are positive Bias are coupled.

The output signal of the summing amplifier is via a line 8o6 is applied to the base of a transistor 808. The collector of transistor 808 is connected to a source through a zener diode 81o connected for positive bias. The transistor 808 is connected to the base of a transistor 812 as an emitter follower. The emitter of transistor 812 is capacitively coupled to the base of a transistor 814. The emitter of the transistor 814 supplies an inverted, realistic deflection control signal via terminal 816. The emitter of the transistor is also directly coupled to a terminal 818 to provide the realistic deflection control signal for non-linear control the vertical deflection of the radar picture tube in the manner described above.

The signal generated at terminal 816 is a derivative of the

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realistic deflection and can be fed to the brightness control and intensity compensation circuit to control the same will.

From the above it is clear that the inventive Radar system provides a high azimuthal resolution for an excellent runway image during the landing approach of an aircraft, while at the same time the simplicity, reliability and value for money of the system are retained. It has "

it turned out that the radar system according to the invention at allows an excellent distance estimate in any weather and that the beam width of 0.4 together with the expanding, lifelike, perspective representation with an excellent resolution for the representation of a runway approached in dense fog or in heavy rain .. That The on-board system according to the invention also enjoys considerable confidence among the pilots, since it is at a reasonable distance creates direct contact with the runway being approached, independent of ground stations, and a system of third category for fast jet engines.

The mechanical scanning resonance antenna according to the invention provides an excellent resolution, leads to a stable, electrical working characteristic and ensures a consistent Beam width, a consistent antenna gain and a consistent azimuth display. The inventive, lifelike, perspective illustration provides an excellent contrast between a runway and the surrounding grass

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areas, whereby in one embodiment of a system according to the invention a contrast in the order of magnitude of 20 dB is obtained became. For weather conditions between heavy fog and rain with a rainfall of 4 mm / hour, a good distinction is achieved between the concrete of the runway and the adjacent grassy areas.

In the event that the runway is flooded or covered in snow, which greatly worsens the contrast between the grassy areas and the runway or even disappears, the radar system according to the invention shows the runway lights through which the Ground runway boundaries established. In this case, the representation can be achieved by using special reflectors with two Jump edges are improved. A suitable reflector with two jump edges reflects the circularly polarized transmission signal in the correct sense for the reception by the system according to the invention.

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Claims (23)

213 A 38 9 54 b -6LSk-. k-146 o6.o7.71 fcs claims 1.) Radar approach system for aircraft with an antenna system, a motor for pivoting the antenna around a center point, a radar transmitter and receiver for transmitting and receiving pulse-shaped radar signals via the antenna and with a display device, characterized in that the antenna has a radiation pattern , which has a vertical beam width that is large enough to see the runway during the approach and which has a horizontal beam width that ensures a high resolution, and that a circuit is provided to control the timing of the display device so that this g provides a realistic, perspective image of the runway approached on the radar screen. 2. landing approach system according to claim 1, characterized in that that the radiation pattern of the antenna has an angle of approximately 17 in the vertical direction. 3. landing approach system according to claim 1, characterized in that - 66 - 109884/1318 2134964 A 38 954 b - & β - k-146
o6.o7.71 that the radiation pattern of the antenna has an angle of less than 1 in the horizontal direction. 4. approach system according to claim 1, characterized in that the antenna in the horizontal direction over an angle is pivoted by about 3o and that the pulse-shaped Radar signals have frequencies in the Ka-band. 5. landing approach system according to claim 1, characterized in that the antenna is an elongated, slotted at the corners Contains semiconductor device, which is arranged horizontally in the aircraft and pivotable about a vertical central axis and that a drive mechanism is provided for pivoting the antenna about the vertical central axis. 6. radar approach system according to claim 1, characterized in that the antenna has an elongated housing which is arranged horizontally movable in the front part of an aircraft, that the housing has a waveguide arrangement slotted at the corners carries, which in turn is arranged in an elongated reflector that has a radiation pattern j produces the narrower in azimuth than in elevation is, and that a motor is provided to the housing and thus the radar beam periodically over a To pivot azimuth angle that is large enough to a runway during a glide slope approach of the aircraft capture. 7. radar approach system according to claim 1, characterized in that - 67 - 109884/1318 A 38 951 b -W- k-146
o6.o7.71 that the display device controlled by the radar receiver a circuit for the non-linear control of the deflection signals for the optical reproduction of the approached runway so that a radar image with a lifelike, linear perspective is generated. 8. Radar approach system according to claim 7, characterized in that it is designed as ι-board system of an aircraft and that is illustrated by means of the deflection of the elevation angle of a target in dependence on the ratio of the height to the aircraft radar distance. 9. radar approach system according to claim 7, characterized in that that means are provided for generating a B-representation by the display device. 10. Radar approach system according to claim 7, characterized in that that the horizontal deflection can be controlled as a function of the azimuth angle of the pivoting of the radar system. 11. Radar approach system according to claim 1, characterized in that that the recording device comprises a radar picture tube, that a horizontal deflection and a vertical deflection is provided, that means for controlling the horizontal deflection are provided in direct dependence on the azimuth angle of the antenna and that control devices the vertical deflection depending on the altitude of the aircraft and the current target distance are provided. - 68 - 109884/1318 A 38 954 b '- 6 * - k-146
o6.o7.71 12. Radar approach system according to claim 11, characterized in that that means for controlling the elevation angle, which is displayed on the radar picture tube, as a function are provided by the ratio of the flight altitude to the respective target distance. 13. Radar approach system according to claim 11, characterized in that the display device which converge towards the rear end of the runway, generated so that the image of a life-like, linear perspective corresponds to a visual representation of the runway with a straight leading edge and having straight side edges _s. 14. Radar approach system according to claim 11, characterized in that devices are provided to adjust the angle of the display on the screen of the radar picture tube as a function of the roll amplitude of the aircraft. 15. Radar approach system according to claim 11, characterized in that the radar picture tube during the landing of the aircraft continuously provides an indication of the desired touchdown point on the runway. 16. Radar approach system according to claim 11, characterized in that that facilities for generating a simulated horizon and sky are provided on the radar screen. 17. Radar approach system according to claim 11, characterized in that that devices for generating distance mark representations - 69 - 109884/1318 213486A A 38 95H b k-146 06.o7.71 fcs lungs are provided on the radar screen. 18. Radar approach system according to claim 11, characterized in that the radar picture tube has an optical display of the lateral Deviation of the aircraft from the center line of the runway delivers. 19. Radar approach system according to claim 5, characterized in that f that switching devices are provided to switch the display device so that it is a PPI or B display supplies. 20. Radar approach system according to claim 7, characterized in that the display device controllable by the radar receiver for generating an optical display of the runway being approached contains a circuit for non-linear control of the deflection signals for the display device, which contains control circuits for the vertical deflection which wave shaper include that change the amplitude of the altitude of the aircraft corresponding signals non-linear, include cherschaltungen further storage A, the non-linear charge in response to the output signals of WeTLenforiner and produced the means for simultaneous summation of the memory circuits Tensions included. A radar approach system according to claim 2o, characterized in that means for controlling the operation of the memory circuits are provided depending on the flight altitude. - 7o - 109884/1318 A 38 954 b - XT - k-146
o6.o7.71 · » 22. Radar approach system according to claim 2o, characterized in that the following wave formers are provided: A first wave shaper that provides an output signal whose amplitude decreases with increasing flight altitude, a second wave shaper, which generates an output signal whose amplitude with increasing flight altitude with a first Slope increases until an amplitude threshold is reached and its amplitude then with increasing flight altitude increases with a smaller slope, a third wave shaper that generates an output signal, whose amplitude increases linearly with increasing flight altitude and a fourth wave shaper, which delivers an output signal whose amplitude is so large that when it is added to the output signals of the first, second and third wave shaper results in a voltage of constant amplitude. 23. Radar approach system according to claim 2o, characterized in that that the memory circuits contain capacities and each have a different charging time constant. 109884/1318